WASHINGTON — The FBI uses drones for surveillance of stationary subjects, and the privacy implications of such operations are "worthy of debate," FBI Director Robert Mueller said Wednesday.

He said the law enforcement agency very seldom uses drones now, but is developing guidelines that will shape how unmanned aerial vehicles are to be used.

There will be a number of issues regarding drones "as they become more omnipresent, not the least of which is the drones in airspace and also the threat on privacy," Mueller said in an appearance before the Senate Judiciary Committee.

"We already have, to a certain extent, a body of law that relates to aerial surveillance and privacy relating to helicopters and small aircraft ... which could well be adapted to the use of drones," Mueller said. "It's still in its nascent stages ... but it's worthy of debate and perhaps legislation down the road."

A member of the Senate Intelligence Committee, Sen. Mark Udall, D-Colo., expressed concern that "the FBI is deploying drone technology while only being in the 'initial stages' of developing guidelines."

Drones allows the FBI to learn critical information that otherwise would be difficult to obtain without introducing serious risk to law enforcement personnel, the law enforcement agency said in a statement following Mueller's comments at the Senate hearing.

The FBI used drones at night during a six-day hostage standoff in Alabama earlier this year. The standoff ended when members of an FBI rescue team stormed an underground bunker, killing gunman Jimmy Lee Dykes before he could harm a 5-year-old boy held hostage.

The FBI said its unmanned aerial vehicles are used only to conduct surveillance operations on stationary subjects. In each instance, the FBI first must obtain the approval of the Federal Aviation Administration to use the aircraft in a very confined geographic area.

The aerospace industry forecasts a worldwide deployment of almost 30,000 drones by 2018, with the United States accounting for half of them.

U.S. stocks are rising for the sixth day in a row Friday as major indexes continue to set records. The largest gains are going to industries that have been mostly left out of the post-election rally, including health care companies and makers of household goods. Banks, which have led that surge, are slipping.

President Barack Obama has ordered intelligence officials to conduct a broad review on the election-season hacking that rattled the presidential campaign and raised new concerns about foreign meddling in U.S. elections, a White House official said Friday.